1. Field of the Invention
The present invention relates to a lithium ion secondary battery, and more particularly to an electrode assembly therefore.
2. Description of the Related Art
As is generally known in the art, a lithium ion secondary battery includes an electrode assembly which has positive and negative electrode collectors coated with active materials of a predetermined thickness and a separator interposed between the collectors and which is wound a number of times into a jelly roll configuration. After being wound a number of times into a jelly roll configuration, the electrode assembly is contained in a cylindrical or square-type can or a pouch and is sealed.
The collectors have conductive tabs welded thereto which extend a predetermined distance to the exterior so that charging electrical power can be applied from the exterior of the battery or discharging electrical power can be applied to the exterior of the battery. Particularly, positive and negative electrode conductive tabs are welded to the positive and negative electrode collectors, respectively. The positive and negative electrode conductive tabs have insulation tape attached to the surface thereof with a predetermined thickness to prevent the separator from being damaged and to avoid a direct short circuit.
The thickness of the collectors is about 10 μm, of the active materials, about 120 μm, of the conductive tabs, about 100 μm, and of the insulation tape, about 40 μm. The total thickness of the conductive taps and the insulation tape is substantially larger than that of the active materials.
When the electrode assembly configured as above is wound into a jelly roll configuration, the wound regions corresponding to the conductive tabs and the insulation tape are substantially thicker than the remaining wound regions. Particularly, the wound regions corresponding to the conductive tabs and the insulation tape protrude further to the exterior than the remaining regions. When the electrode assembly is inserted into a can or pouch, therefore, such irregular thickness makes the insertion of the electrode assembly difficult, sometimes causing the protruding portions to deform. Such deformation may decrease the battery capacity.
Since the electrode assembly is not easily insertable into a can, it may be pressed or squeezed to achieve the desired result. As a result, the active materials corresponding to the lower conductive tap and the insulation tape are then compressed by a strong force and may have degraded usefulness in those parts. In other words, the active materials may have little use but still increase the thickness of the electrode assembly.
Accordingly, there is a need for an electrode assembly having a reduced overall winding thickness and a lithium ion secondary battery using the same.